There are a number of less common types of re-locker devices. For example, high-security safes sometimes come with ”glass relockers”. There is typically a piece of tempered glass with two holes in it, and wires under spring tension are hooked into the holes. If a person pounds on the lock it will shatter the glass, causing the relock pin to snap into place, which blocks the safe boltworks from being forced open. Hitting the glass with a drill bit will also break the glass.
Thermal relockers are found only on high end, high-security safes. Normally there is a piece of metal or a soldered piece in a wire arrangement, all under spring pressure. The metal melts at a very low temperature, maybe 250 degrees. Heat generated from a torch, or even from extensive grinding, will melt the metal which sets off the relocker.
Some relockers do not actually block the boltworks from moving. On some units firing a relocker causes a heavy bolt to shoot out from the door, behind the frame of the safe. This is great way of keeping the door from being forced open. The photo shows a unique system: The relock can be fired either by an attack on the lock, by a torch cutting through the cable, or by melting the soldered thermal joint just above the lock encasement. When set off this is actually a double relocker. One part (not shown) blocks the right side boltworks from moving. The vertical bolt shoots out about an inch — this is accomplished with a heavy spring which can’t be seen here. It is then behind the door opening of the safe body where it very stubbornly keeps the safe door closed.
Once again, only experienced safe technicians should work on your safe. Inexperienced technicians may accidentally set off a relocker, perhaps costing you hundreds of dollars.